Manures, Fertilizers, and Soil Fertility Management Notes

Classification and Properties of Organic Manures

• Organic manures are substances of plant or animal origin that contain large proportions of organic matter and small quantities of plant nutrients compared to chemical fertilizers.

• Bulky Organic Manures: Includes Farm Yard Manure (FYM), compost, and green manure. They supply O.M. to improve physical, chemical, and biological soil properties.

• Concentrated Organic Manures: Includes oil cakes, blood meal, and fish manure. These contain higher percentages of $N$, $P_2O_5$, and $K_2O$ than bulky manures.

• Farm Yard Manure (FYM): A decomposed mixture of dung, urine, animal bedding, and left-over fodder. Well-rotted FYM contains $0.5\% N$, $0.2\% P_2O_5$, and $0.5\% K_2O$.

• Urine: Contains a higher percentage of $N$ and $K_2O$ compared to dung. Nitrogen is often lost from urine via the formation of gaseous $NH_3$ from urea.

Compost and Vermicomposting

• Composting: A biochemical process where microorganisms decompose organic residue to lower the $C:N$ ratio. Final products are rural compost (farm litter) or urban compost (town refuse).

• Mechanical Composting: Urban plants produce compost with approximately $0.7\% N$, $0.5\% P_2O_5$, and $0.4\% K_2O$ with a $C:N$ ratio of $15-17$.

• Vermicomposting: Utilizes earthworm species like Red Wigglers (Eisenia foetida) to break down waste. Vermicompost contains $1.6\% N$, $0.7\% P$, $0.8\% K$, and $0.5\% Ca$.

• Night Soil: Human excrement containing $5.5\% N$, $4.0\% P_2O_5$, and $2.0\% K_2O$ on an oven-dry basis. It is often handled via the Poudrette System.

• Sewage and Sludge: Sewage is $99.0\%$ water. Sludge (solid portion) is separated; when oxidized, it is called activated sludge, containing $3-6\% N$, $2\% P_2O_5$, and $1\% K_2O$.

Transformation Reactions and $C:N$ Ratio

• Mineralization: The microbial conversion of organic nitrogen into inorganic forms ($NH_4^+$ and $NO_3^-$).

• Immobilization: Microorganisms convert inorganic nutrients ($NO_3^-$, $NH_4^+$) back into unavailable organic forms (protein/metabolism) when carbon-rich residues are added.

• $C:N$ Ratio Importance: Humus has a ratio of approximately $10:1$. Arable soils range from $8:1$ to $15:1$. A wide ratio ($35:1$ or higher) results in slow decomposition and nitrogen deficiency for plants as microbes compete for available $N$.

• Nitrification: A two-step biological oxidation of $NH_4^+$ to $NO_2^-$ (by Nitrosomonas) and then to $NO_3^-$ (by Nitrobactor).

Integrated Nutrient Management (INM)

• INM Concept: The maintenance of soil fertility and agricultural productivity through the judicious use of mineral fertilizers, organic manures, farm wastes, and biofertilizers.

• Objectives: Enhancing fertilizer use efficiency (NUE) and sustaining soil health while meeting the heavy nutrient demands of high-yielding crop varieties.

• Biofertilizers: Includes Rhizobium (symbiotic $N$ fixation in legumes), Azotobacter (non-symbiotic), Azospirillum, Blue green algae, and Azolla.

Chemical Fertilizers: Classification and Properties

• Nitrogenous Fertilizers: Classified into Nitrate ($NaNO_3$, $16\% N$), Ammoniacal ($(NH_4)_2SO_4$, $20.6\% N$), Nitrate and Ammoniacal ($CAN$, $26\% N$), and Amide (Urea, $46\% N$).

• Phosphatic Fertilizers:

  • Water-soluble: Single Super Phosphate (SSP, $16\% P_2O_5$) and Triple Super Phosphate (TSP, $48\% P_2O_5$).

  • Citrate-soluble: Basic slags ($14-18\% P_2O_5$) and Dicalcium phosphate.

  • Insoluble: Rock phosphate ($20-40\% P_2O_5$).

• Potassic Fertilizers: Muriate of Potash ($KCl$, $60\% K_2O$) and Potassium sulphate ($K_2SO_4$, $48\% K_2O$).

• Secondary/Micronutrients: Secondary nutrients are $Ca$, $Mg$, and $S$. Micronutrients (trace elements) include $Zn$, $Fe$, $Cu$, $Mn$, $B$, $Mo$, and $Cl$.

• Nano-Fertilizers: Nutrients encapsulated or coated at the nanoscale to enhance uptake and reduce environmental losses like leaching or volatilization.

Soil Fertility and Productivity

• Soil Fertility: The inherent capacity of the soil to supply essential nutrients in right proportions and quantities.

• Soil Productivity: The ability of a soil to produce crop yields under specific management ($Productivity = f(Fertility, Management, Environment)$).

• Criteria of Essentiality (Arnon, 1954): An element is essential if the plant cannot complete its life cycle without it, the element is non-replaceable, and it plays a direct role in metabolism.

• Law of Minimum (Liebig): Crop yield is limited by the essential nutrient present in the lowest amount relative to the plant's needs.

Soil Testing and Plant Analysis

• Soil Testing: Chemical analysis to determine available nutrients. Critical levels for low status: Alkaline KMnO_4-N < 250\,kg/ha, Olsen's P_2O_5 < 28\,kg/ha, and Neutral NH_4OAc-K_2O < 140\,kg/ha.

• Plant Analysis: Diagnostic tool calculating nutrient concentrations in tissue. Critical level is the concentration where yield begins to decline significantly.

• STCR (Soil Test Crop Response): A rationalized fertilizer recommendation approach considering soil contribution, fertilizer contribution, and specific target yields.

Soil Amendments

• Alkali Soils: Reclaimed using Gypsum ($CaSO_4 \cdot 2H_2O$) to replace exchangeable $Na^+$. Other amendments include sulfur, pyrites, and green manuring with Sesbania aculeata (Dhaincha).

• Acidic Soils: Reclaimed using Liming materials like Calcitic limestone ($CaCO_3$) or Dolomitic limestone ($CaMg(CO_3)_2$).

• Gypsum is not a liming material because its anion (sulphate) produces mineral acid ($H_2SO_4$) which can increase acidity.

Fertilizer Control Order (FCO)

• Fertilizer (Control) Order 1985: Strictly regulates the quality, trade, and price of fertilizers. It classifies fertilizers as Essential Commodities.

• Specifications: FCO sets maximum moisture levels (e.g., $1.0\%$ for Urea), minimum nutrient contents, and impurity limits (e.g., Biuret in urea must not exceed $1.5\%$).

• Organic manures are substances of plant or animal origin that contain large proportions of organic matter and small quantities of plant nutrients compared to chemical fertilizers.

• Bulky Organic Manures: Examples include:

  • Farm Yard Manure (FYM): A decomposed mixture of dung, urine, animal bedding, and left-over fodder. Well-rotted FYM contains 0.5 ext{% N}, 0.2 ext{% P}2O5, and 0.5 ext{% K}_2O.

  • Compost: Made from organic waste such as food scraps, yard waste, and plant material.

  • Green Manure: Leguminous crops like clover and alfalfa that are plowed into the soil to increase fertility.

• Concentrated Organic Manures: Examples include:

  • Oil Cakes: Byproducts from oil extraction, high in nutrients.

  • Blood Meal: A dry, powdery product made from animal blood, rich in nitrogen.

  • Fish Manure: Nutrient-rich byproduct from fish processing.

• Vermicompost: Contains 1.6 ext{% N}, 0.7 ext{% P}, 0.8 ext{% K}, and 0.5 ext{% Ca} produced by earthworm digestion of organic material.

• Night Soil: Human excrement containing 5.5 ext{% N}, 4.0 ext{% P}2O5, and 2.0 ext{% K}_2O on an oven-dry basis. It is often managed using the Poudrette System.

• Sewage and Sludge: Sewage is 99.0 ext{%} water, and oxidized sludge is called activated sludge containing 3-6 ext{% N}, 2 ext{% P}2O5, and 1 ext{% K}_2O.

• Night Soil: Human excrement containing 5.5 ext{% N}, 4.0 ext{% P}2O5, and 2.0 ext{% K}_2O on an oven-dry basis. It is often handled via the Poudrette System.